Utilities, including electrical, water and gas utilities monitor consumption by customers through meters. In particular, electrical utilities monitor electrical energy consumption, water utilities monitor water consumption, and gas utilities monitor gas consumption. Utilities use the consumption information primarily for billing, but also for resource allocation planning and other purposes.
Modern utility meters typically include numerous solid state electronics components and associated electronic devices including sensor devices, data processors, microcontrollers, memory devices, clocks, and communications devices. These electronic devices are used for various purposes within the meter, including usage detection, consumption calculation, data storage, and communications. In association with these electronic devices, the utility meters also include a power supply configured to provide DC power to the electronic devices.
A typical onboard power supply utilized in electricity meters is a wide range switching power supply. A single wide range switching power supply may supply the power for both the data acquisition hardware and the communications hardware. Switching power supplies store DC energy in capacitors. The DC energy stored in the capacitors is typically used to sustain the operation of the meter for some limited amount of time in the event of a power-down event. For example, some capacitors associated with the switching power supply may be configured to provide DC power to the microcontroller until the non-volatile memory write cycle is completed (approx. 400 mS) during power outages. The power provided from the capacitor for this short amount of time allows for the recording of energy consumption data which would otherwise be lost in the event of a power outage.
Another example of a capacitor sometimes associated with the power supply is an electric double-layer capacitor (i.e., a “super capacitor”) used to provide DC power to the real time clock in the absence of a lithium battery. Super capacitors are characterized by long life and a high energy density. In the event of a power outage in the electricity meter, the super capacitor is configured to provide DC power to the real time clock for a relatively long period of time (e.g., thirty six hours to seventy two hours or more). By supplying power to the real time clock during a power outage, the electricity meter maintains the proper time even if power is not restored to the meter for several hours or days.
Super capacitors used in electricity meters are normally charged off the regulated voltage of the power supply using a simple current limiting resistor without any circuit delays. In order to minimize the burden on the DC power supply, the current available to charge the super capacitor is typically limited down to a few milliamps at the expense of long charge times (e.g., in the order of 10 to 15 minutes). However, longer charge times mean that the super capacitor may not fully charge following power-up if a power outage occurs. Long charge times also impose a significant burden on the meter manufacturing/programming/testing when the supercap charging circuit needs to be verified. For instance during the electronics assembly process each functional block needs to be exercised which means that a significant delay will be introduced at low charging currents to verify the correct operation of the charging circuit. Thus, a need exists for a utility meter configured to economically facilitate rapid charge times for the super capacitor without imposing a significant burden on the power supply.